In the field of matrix printers, it is, of course, well known that a printer may include one or more print heads which are caused to be moved in a reciprocating manner across the printer for printing in serial fashion. The print head may be moved by a cable and pulley arrangement, a lead screw, or a cam drive or like drive mechanism. Each of the print heads includes a plurality of printing elements supported in a group and each of the elements is actuated or energized at high speed to cause printing of dots in a matrix character by movement of dot-making elements including droplets of ink or printing wires, attached to the printing elements, and wherein the wires or droplets are caused to be impacted against the paper. The print wires or ink jet nozzles are usually closely spaced in vertical manner so as to print the dots which make up the characters as the print heads are moved across the printer. In this manner, a line of printed characters is completed upon travel of the print head in one direction across the paper. Printing may also be performed in the other direction if the required controls are included in the printer.
Another form of matrix printer includes the use of a plurality of printing elements supported from a carriage in a manner wherein the printing elements are aligned horizontally across the printer and upon each pass of the carriage, respective dots of characters are printed in a line or row and subsequent passes of the carriage and printing elements cause additional lines of dots to be printed to complete the dot matrix characters in the line of printing. Common arrangements include the use of four or eight printing elements supported from the carriage.
A timing strip with slots or like indicia is commonly used to dictate actuation of the printing elements wherein one or more sensors sense the slots or other indicia to print dots in precise columns across the paper. While the printing has usually been performed in one direction, for example, left to right, it is more recently that printing has been done in both directions of travel of the printing element carriage.
The control systems for matrix printers have included input converters, shift registers, buffer storage, character generators and solenoid or other print element drivers for printing a line of dots in successive manner across the paper to form a line of characters.
Representative prior art relating to control systems for matrix printers include U.S. Pat. No. 3,703,949 issued to R. Howard et al. on Nov. 28, 1972, wherein input information is loaded into a buffer in parallel and printing does not begin until the buffer is loaded to print a complete line. Detection of the location of the carriage moving the print head is performed independent of the carriage to actuate the print wires at the appropriate locations.
U.S. Pat. No. 3,719,781 issued to J. R. Fulton et al. on Mar. 6, 1973, shows a control system having a line relay for receiving the input signal, an input clock and a shift register as a buffer store, an operational store, a load detector, and operational control means to actuate the printer.
U.S. Pat. No. 3,789,969 issued to R. Howard et al. On Feb. 5, 1974, shows a control system wherein input data is fed in parallel into a multistage shift register, the output going to a character generator to provide signals representing a line of dots for the characters to be printed, and which trigger the operation of the print wire solenoids.
U.S. Pat. No. 3,833,891 issued to R. Howard et al. on Sept. 3, 1974 shows input data into a multistage shift register, selected stages of the register applied to a character generator to form signals representing the top line of characters to trigger operation of the print wire solenoids.
U.S. Pat. No. 3,834,304 issued to J. T. Potter on Sept. 10, 1974 shows logic circuits which include a read only memory for storing signal sets representing dot patterns to be printed in rows. The sets are read out to shift registers to control actuation of the hammers.
U.S. Pat. No. 3,858,703 issued to H. Duley on Jan. 7, 1975 discloses a bi-directional dual head printer which uses a registration strip with a plurality of equally spaced narrow transparent slots and wherein a recirculating shift register stores all of the characters until a full line of characters is printed.
U.S. Pat. No. 3,941,051 issued to G. B. Barrus et al. on Mar. 2, 1976, shows a printer system of bi-directional printing wherein a reciprocating shuttle system forms part of a dynamically balanced system wherein a cam motion engages an oppositely moving counterweight system.
U.S. Pat. No. 3,970,183 issued to P. Robinson on July 20, 1976 shows a bi-directional printer wherein monitoring is performed by detecting both the direction of print head movement and print head position at any time. Information is detected by a pair of optical channels and the registration strip has a pair of displaced sets of transparent slots therein. Circuitry is provided for storing data representing the next line to be printed in both the forward and the reverse formats.
U.S. Pat. No. 3,991,868 issued to P. Robinson et al. on Nov. 16, 1976 discloses printing of double and triple sized characters in segments which are stored in readable memories. The apparatus comprises a shift register having a plurality of stages equal to the number of standard size characters capable of being printed along a single line.
U.S. Pat. No. 4,024,506 issued to H. Spaargaren on May 17, 1977 shows control devices which include a starting position device, an address counter, a buffer store, a character generator and a row counter and column counter.
And, U.S. Pat. No. 4,026,402 issued to W. J. Byrd on May 31, 1977 shows a line printer which provides for either a single character or a burst of characters and a registration system serves the dual function of locating the proper position for a character to be printed and determining the direction of movement of the print head. A storage capability is in a recirculating memory and the data memory is a multistage shaft register which tracks the data in the recirculating memory.